Semi-Batch and Batch Low-Salt-Rejection Reverse Osmosis for Brine Concentration

Abstract

Brine management strategies require efficient methods of desalinating high-salinity streams (> 7 wt%). While reverse osmosis (RO) systems have been proposed to desalinate high-saline streams, the osmotic pressure exceeds the burst pressure of the RO membranes. To circumvent this issue, low-salt rejection RO (LSRRO) systems are introduced to provide salt leakage through the membranes. However, the energy needed to desalinate high-saline streams is significant (e.g., > 5 kWh/m3 for treating seawater stream). In this work, we develop a novel transient multistage processes (i.e., semi-batch and batch) that employs LSRRO membranes to desalinate high-saline streams. Herein, we use a simplified lumped model to capture the system performance under ideal and non-ideal conditions, and optimize salt rejection per pass for the multistage system. The modeling results show multistage batch system significantly outperforms the steady-state LSRRO by reducing energy consumption by 38% to 73%. In particular, the ZLD application for 4-stage batch system requires energy consumption between 1.07 and 6.96 kWh/m3 for the feed salinity range of 0.1 and 1 mol/L. The SB-LSRRO system is constrained by the loss due to the mixing of streams which results in more stages and higher energy consumption than SB-LSRRO.

Keywords: Low salt rejection, Reverse Osmosis, Batch process, High salinity, spiral wound membrane